Method and apparatus for transmitting cell shaping indication in wireless communication system

ABSTRACT

A method and apparatus for transmitting a cell shaping/un-shaping indication in a wireless communication system is provided. A first eNodeB (eNB) transmits a cell shaping/un-shaping indication which indicates cell shaping/un-shaping of a cell, managed by the first eNB, in an active antenna system (AAS) to a second eNB. The cell shaping means that main coverage of the cell is maintained unchanged but an edge of the cell can be adapted to load demand. The cell un-shaping means that coverage of the cell goes back to original coverage.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for transmitting a cell shapingindication in a wireless communication system.

Related Art

Universal mobile telecommunications system (UMTS) is a 3rd generation(3G) asynchronous mobile communication system operating in wideband codedivision multiple access (WCDMA) based on European systems, globalsystem for mobile communications (GSM) and general packet radio services(GPRS). The long-term evolution (LTE) of UMTS is under discussion by the3rd generation partnership project (3GPP) that standardized UMTS.

The 3GPP LTE is a technology for enabling high-speed packetcommunications. Many schemes have been proposed for the LTE objectiveincluding those that aim to reduce user and provider costs, improveservice quality, and expand and improve coverage and system capacity.The 3GPP LTE requires reduced cost per bit, increased serviceavailability, flexible use of a frequency band, a simple structure, anopen interface, and adequate power consumption of a terminal as anupper-level requirement.

FIG. 1 shows LTE system architecture. The communication network iswidely deployed to provide a variety of communication services such asvoice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or moreuser equipment (UE; 10), an evolved-UMTS terrestrial radio accessnetwork (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers toa communication equipment carried by a user. The UE 10 may be fixed ormobile, and may be referred to as another terminology, such as a mobilestation (MS), a user terminal (UT), a subscriber station (SS), awireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and aplurality of UEs may be located in one cell. The eNB 20 provides an endpoint of a control plane and a user plane to the UE 10. The eNB 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as a base station (BS), a basetransceiver system (BTS), an access point, etc. One eNB 20 may bedeployed per cell. There arc one or more cells within the coverage ofthe eNB 20. A single cell is configured to have one of bandwidthsselected from 1.25, 2.5, 5, 10, and 20 MHz, etc., and provides downlinkor uplink transmission services to several UEs. In this case, differentcells can be configured to provide different bandwidths.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10, and an uplink (UL) denotes communication from the UE 10 tothe eNB 20. In the DL, a transmitter may be a part of the eNB 20, and areceiver may be a part of the UE 10. In the UL, the transmitter may be apart of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) which is in chargeof control plane functions, and a system architecture evolution (SAE)gateway (S-GW) which is in charge of user plane functions. The MME/S-GW30 may be positioned at the end of the network and connected to anexternal network. The MME has UE access information or UE capabilityinformation, and such information may be primarily used in UE mobilitymanagement. The S-GW is a gateway of which an endpoint is an E-UTRAN.The MME/S-GW 30 provides an end point of a session and mobilitymanagement function for the UE 10. The EPC may further include a packetdata network (PDN) gateway (PDN-GW). The PDN-GW is a gateway of which anendpoint is a PDN.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, Inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), P-GW and S-GW selection,MME selection for handovers with MME change, serving GPRS support node(SGSN) selection for handovers to 2G or 3G 3GPP access networks,roaming, authentication, bearer management functions including dedicatedbearer establishment, support for public warning system (PWS) (whichincludes earthquake and tsunami warning system (ETWS) and commercialmobile alert system (CMAS)) message transmission. The S-GW host providesassorted functions including per-user based packet filtering (by e.g.,deep packet inspection), lawful interception, UE Internet protocol (IP)address allocation, transport level packet marking in the DL, UL and DLservice level charging, gating and rate enforcement, DL rate enforcementbased on APN-AMBR. For clarity MME/S-GW 30 will be referred to hereinsimply as a “gateway,” but it is understood that this entity includesboth the MME and S-GW.

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 and the eNB 20 are connected by means of a Uu interface. TheeNBs 20 are interconnected by means of an X2 interface. Neighboring eNBsmay have a meshed network structure that has the X2 interface. The eNBs20 are connected to the EPC by means of an S1 interface. The eNBs 20 arcconnected to the MME by means of an S1-MME interface, and are connectedto the S-GW by means of S1-U interface. The S1 interface supports amany-to-many relation between the eNB 20 and the MME/S-GW.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and atypical EPC. Referring to FIG. 2, the eNB 20 may perform functions ofselection for gateway 30, routing toward the gateway 30 during a radioresource control (RRC) activation, scheduling and transmitting of pagingmessages, scheduling and transmitting of broadcast channel (BCH)information, dynamic allocation of resources to the UEs 10 in both ULand DL, configuration and provisioning of eNB measurements, radio hearercontrol, radio admission control (RAC), and connection mobility controlin LTE_ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE_IDLE state management,ciphering of the user plane, SAE bearer control, and ciphering andintegrity protection of NAS signaling.

FIG. 3 shows a block diagram of a user plane protocol stack and acontrol plane protocol stack of an LTE system. FIG. 3-(a) shows a blockdiagram of a user plane protocol stack of an LTE system, and FIG. 3-(b)shows a block diagram of a control plane protocol stack of an LTEsystem.

Layers of a radio interface protocol between the UE and the E-UTRAN maybe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. The radio interface protocol between the UE and the E-UTRAN maybe horizontally divided into a physical layer, a data link layer, and anetwork layer, and may be vertically divided into a control plane(C-plane) which is a protocol stack for control signal transmission anda user plane (U-plane) which is a protocol stack for data informationtransmission. The layers of the radio interface protocol exist in pairsat the UE and the E-UTRAN, and are in charge of data transmission of theUu interface.

A physical (PHY) layer belongs to the L1. The PHY layer provides ahigher layer with an information transfer service through a physicalchannel. The PHY layer is connected to a medium access control (MAC)layer, which is a higher layer of the PHY layer, through a transportchannel. A physical channel is mapped to the transport channel. Data istransferred between the MAC layer and the PHY layer through thetransport channel. Between different PHY layers, i.e., a PHY layer of atransmitter and a PHY layer of a receiver, data is transferred throughthe physical channel using radio resources. The physical channel ismodulated using an orthogonal frequency division multiplexing (OFDM)scheme, and utilizes time and frequency as a radio resource.

The PHY layer uses several physical control channels. A physicaldownlink control channel (PDCCH) reports to a UE about resourceallocation of a paging channel (PCH) and a downlink shared channel(DL-SCH), and hybrid automatic repeat request (HARQ) information relatedto the DL-SCH. The PDCCH may carry a UL grant for reporting to the UEabout resource allocation of UL transmission. A physical control formatindicator channel (PCFICH) reports the number of OFDM symbols used forPDCCHs to the UE, and is transmitted in every subframe. A physicalhybrid ARQ indicator channel (PHICH) carries an HARQ acknowledgement(ACK)/non-acknowledgement (NACK) signal in response to UL transmission.A physical uplink control channel (PUCCH) carries UL control informationsuch as HARQ ACK/NACK for DL transmission, scheduling request, and CQI.A physical uplink shared channel (PUSCH) carries a UL-uplink sharedchannel (SCH).

FIG. 4 shows an example of a physical channel structure.

A physical channel consists of a plurality of subframes in time domainand a plurality of subcarriers in frequency domain. One subframeconsists of a plurality of symbols in the time domain. One subframeconsists of a plurality of resource blocks (RBs). One RB consists of aplurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use specific subcarriers of specific symbols of acorresponding subframe for a PDCCH. For example, a first symbol of thesubframe may be used for the PDCCH. The PDCCH carries dynamic allocatedresources, such as a physical resource block (PRB) and modulation andcoding scheme (MCS). A transmission time interval (TTI) which is a unittime for data transmission may be equal to a length of one subframe. Thelength of one subframe may be 1 ms.

The transport channel is classified into a common transport channel anda dedicated transport channel according to whether the channel is sharedor not. A DL transport channel for transmitting data from the network tothe UE includes a broadcast channel (BCH) for transmitting systeminformation, a paging channel (PCH) for transmitting a paging message, aDL-SCH for transmitting user traffic or control signals, etc. The DL-SCHsupports HARQ, dynamic link adaptation by varying the modulation, codingand transmit power, and both dynamic and semi-static resourceallocation. The DL-SCH also may enable broadcast in the entire cell andthe use of beamforming. The system information carries one or moresystem information blocks. All system information blocks may betransmitted with the same periodicity. Traffic or control signals of amultimedia broadcast/multicast service (MBMS) may be transmitted throughthe DL-SCH or a multicast channel (MCH).

A UL transport channel for transmitting data from the UE to the networkincludes a random access channel (RACH) for transmitting an initialcontrol message, a UL-SCH for transmitting user traffic or controlsignals, etc. The UL-SCH supports HARQ and dynamic link adaptation byvarying the transmit power and potentially modulation and coding. TheUL-SCH also may enable the use of beamforming. The RACH is normally usedfor initial access to a cell.

A MAC layer belongs to the L2. The MAC layer provides services to aradio link control (RLC) layer, which is a higher layer of the MAClayer, via a logical channel. The MAC layer provides a function ofmapping multiple logical channels to multiple transport channels. TheMAC layer also provides a function of logical channel multiplexing bymapping multiple logical channels to a single transport channel. A MACsublayer provides data transfer services on logical channels.

The logical channels are classified into control channels fortransferring control plane information and traffic channels fortransferring user plane information, according to a type of transmittedinformation. That is, a set of logical channel types is defined fordifferent data transfer services offered by the MAC layer. The logicalchannels are located above the transport channel, and are mapped to thetransport channels.

The control channels are used for transfer of control plane informationonly. The control channels provided by the MAC layer include a broadcastcontrol channel (BCCH), a paging control channel (PCCH), a commoncontrol channel (CCCH), a multicast control channel (MCCH) and adedicated control channel (DCCH). The BCCH is a downlink channel forbroadcasting system control information. The PCCH is a downlink channelthat transfers paging information and is used when the network does notknow the location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting MBMS control information from the networkto a UE. The DCCH is a point-to-point bi-directional channel used by UEshaving an RRC connection that transmits dedicated control informationbetween a UE and the network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by the MAC layer include a dedicatedtraffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCHis a point-to-point channel, dedicated to one UE for the transfer ofuser information and can exist in both uplink and downlink. The MTCH isa point-to-multipoint downlink channel for transmitting traffic datafrom the network to the UE.

Uplink connections between logical channels and transport channelsinclude the DCCH that can be mapped to the UL-SCH, the DTCH that can bemapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH.Downlink connections between logical channels and transport channelsinclude the BCCH that can be mapped to the BCH or DL-SCH, the PCCH thatcan be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, andthe DTCH that can be mapped to the DL-SCH, the MCCH that can be mappedto the MCH, and the MTCH that can be mapped to the MCH.

An RLC layer belongs to the L2. The RLC layer provides a function ofadjusting a size of data, so as to be suitable for a lower layer totransmit the data, by concatenating and segmenting the data receivedfrom a higher layer in a radio section. In addition, to ensure a varietyof quality of service (QoS) required by a radio bearer (RB), the RLClayer provides three operation modes, i.e., a transparent mode (TM), anunacknowledged mode (UM), and an acknowledged mode (AM). The AM RLCprovides a retransmission function through an automatic repeat request(ARQ) for reliable data transmission. Meanwhile, a function of the RLClayer may be implemented with a functional block inside the MAC layer.In this case, the RLC layer may not exist.

A packet data convergence protocol (PDCP) layer belongs to the L2. ThePDCP layer provides a function of header compression function thatreduces unnecessary control information such that data being transmittedby employing IP packets, such as IPv4 or IPv6, can be efficientlytransmitted over a radio interface that has a relatively smallbandwidth. The header compression increases transmission efficiency inthe radio section by transmitting only necessary information in a headerof the data. In addition, the PDCP layer provides a function ofsecurity. The function of security includes ciphering which preventsinspection of third parties, and integrity protection which preventsdata manipulation of third parties.

A radio resource control (RRC) layer belongs to the L3. The RLC layer islocated at the lowest portion of the L3, and is only defined in thecontrol plane. The RRC layer takes a role of controlling a radioresource between the UE and the network. For this, the UE and thenetwork exchange an RRC message through the RRC layer. The RRC layercontrols logical channels, transport channels, and physical channels inrelation to the configuration, reconfiguration, and release of RBs. AnRB is a logical path provided by the L1 and L2 for data delivery betweenthe UE and the network. That is, the RB signifies a service provided theL2 for data transmission between the UE and E-UTRAN. The configurationof the RB implies a process for specifying a radio protocol layer andchannel properties to provide a particular service and for determiningrespective detailed parameters and operations. The RB is classified intotwo types, i.e., a signaling RB (SRB) and a data RB (DRB). The SRB isused as a path for transmitting an RRC message in the control plane. TheDRB is used as a path for transmitting user data in the user plane.

Referring to FIG. 3-(a), the RLC and MAC layers (terminated in the eNBon the network side) may perform functions such as scheduling, automaticrepeat request (ARQ), and hybrid automatic repeat request (HARQ). ThePDCP layer (terminated in the eNB on the network side) may perform theuser plane functions such as header compression, integrity protection,and ciphering.

Referring to FIG. 3-(b), the RLC and MAC layers (terminated in the eNBon the network side) may perform the same functions for the controlplane. The RRC layer (terminated in the eNB on the network side) mayperform functions such as broadcasting, paging, RRC connectionmanagement, RB control, mobility functions, and UE measurement reportingand controlling. The NAS control protocol (terminated in the MME ofgateway on the network side) may perform functions such as a SAE bearermanagement, authentication, LTE_IDLE mobility handling, pagingorigination in LTE_IDLE, and security control for the signaling betweenthe gateway and UE.

An RRC state indicates whether an RRC layer of the UE is logicallyconnected to an RRC layer of the E-UTRAN. The RRC state may be dividedinto two different states such as an RRC connected state and an RRC idlestate. When an RRC connection is established between the RRC layer ofthe UE and the RRC layer of the E-UTRAN, the UE is in RRC_CONNECTED, andotherwise the UE is in RRC_IDLE. Since the UE in RRC CONNECTED has theRRC connection established with the E-UTRAN, the E-UTRAN may recognizethe existence of the UE in RRC_CONNECTED and may effectively control theUE. Meanwhile, the UE in RRC_IDLE may not be recognized by the E-UTRAN,and a CN manages the UE in unit of a TA which is a larger area than acell. That is, only the existence of the UE in RRC_IDLE is recognized inunit of a large area, and the UE must transition to RRC_CONNECTED toreceive a typical mobile communication service such as voice or datacommunication.

In RRC_IDLE state, the UE may receive broadcasts of system informationand paging information while the UE specifies a discontinuous reception(DRX) configured by NAS, and the UE has been allocated an identification(ID) which uniquely identifies the UE in a tracking area and may performpublic land mobile network (PLMN) selection and cell re-selection. Also,in RRC_IDLE state, no RRC context is stored in the eNB.

In RRC_CONNECTED state, the UE has an E-UTRAN RRC connection and acontext in the E-UTRAN, such that transmitting and/or receiving datato/from the eNB becomes possible. Also, the UE can report channelquality information and feedback information to the eNB. InRRC_CONNECTED state, the E-UTRAN knows the cell to which the UE belongs.Therefore, the network can transmit and/or receive data to/from UE, thenetwork can control mobility (handover and inter-radio accesstechnologies (RAT) cell change order to GSM EDGE radio access network(GERAN) with network assisted cell change (NACC)) of the UE, and thenetwork can perform cell measurements for a neighboring cell.

In RRC_IDLE state, the UE specifies the paging DRX cycle. Specifically,the UE monitors a paging signal at a specific paging occasion of everyUE specific paging DRX cycle. The paging occasion is a time intervalduring which a paging signal is transmitted. The UE has its own pagingoccasion.

A paging message is transmitted over all cells belonging to the sametracking area. If the UE moves from one TA to another TA, the UE willsend a tracking area update (TAU) message to the network to update itslocation.

When the user initially powers on the UE, the UE first searches for aproper cell and then remains in RRC IDLE in the cell. When there is aneed to establish an RRC connection, the UE which remains in RRC_IDLEestablishes the RRC connection with the RRC of the E-UTRAN through anRRC connection procedure and then may transition to RRC_CONNECTED. TheUE which remains in RRC_IDLE may need to establish the RRC connectionwith the E-UTRAN when uplink data transmission is necessary due to auser's call attempt or the like or when there is a need to transmit aresponse message upon receiving a paging message from the E-UTRAN.

It is known that different cause values may be mapped o the signaturesequence used to transmit messages between a UE and eNB and that eitherchannel quality indicator (CQI) or path loss and cause or message sizeare candidates for inclusion in the initial preamble.

When a UE wishes to access the network and determines a message to betransmitted, the message may be linked to a purpose and a cause valuemay be determined. The size of the ideal message may be also bedetermined by identifying all optional information and differentalternative sizes, such as by removing optional information, or analternative scheduling request message may be used.

The UE acquires necessary information for the transmission of thepreamble, UL interference, pilot transmit power and requiredsignal-to-noise ratio (SNR) for the preamble detection at the receiveror combinations thereof. This information must allow the calculation ofthe initial transmit power of the preamble. It is beneficial to transmitthe UL message in the vicinity of the preamble from a frequency point ofview in order to ensure that the same channel is used for thetransmission of the message.

The UE should take into account the UL interference and the UL path lossin order to ensure that the network receives the preamble with a minimumSNR. The UL interference can be determined only in the eNB, andtherefore, must be broadcast by the eNB and received by the UE prior tothe transmission of the preamble. The UL path loss can be considered tobe similar to the DL path loss and can be estimated by the UE from thereceived RX signal strength when the transmit power of some pilotsequence of the cell is known to the UE.

The required UL SNR for the detection of the preamble would typicallydepend on the eNB configuration, such as a number of Rx antennas andreceiver performance. There may he advantages to transmit the ratherstatic transmit power of the pilot and the necessary UL SNR separatelyfrom the varying UL interference and possibly the power offset requiredbetween the preamble and the message.

The initial transmission power of the preamble can be roughly calculatedaccording to the following formula:

Transmit power=TransmitPilot−RxPilot+ULInterference+Offset+SNRRequired

Therefore, any combination of SNRRequired, ULInterference, TransmitPilotand Offset can be broadcast. In principle, only one value must bebroadcast. This is essentially in current UMTS systems, although the ULinterference in 3GPP LTE will mainly be neighboring cell interferencethat is probably more constant than in UMTS system.

The UE determines the initial UL transit power for the transmission ofthe preamble as explained above. The receiver in the eNB is able toestimate the absolute received power as well as the relative receivedpower compared to the interference in the cell. The eNB will consider apreamble detected if the received signal power compared to theinterference is above an eNB known threshold.

The UE performs power ramping in order to ensure that a UE can bedetected even if the initially estimated transmission power of thepreamble is not adequate. Another preamble will most likely betransmitted if no ACK or NACK is received by the UE before the nextrandom access attempt. The transmit power of the preamble can beincreased, and/or the preamble can be transmitted on a different ULfrequency in order to increase the probability of detection. Therefore,the actual transmit power of the preamble that will be detected does notnecessarily correspond to the initial transmit power of the preamble asinitially calculated by the UE.

The UE must determine the possible UL transport format. The transportformat, which may include MCS and a number of resource blocks thatshould be used by the UE, depends mainly on two parameters, specificallythe SNR at the eNB and the required size of the message to betransmitted.

In practice, a maximum UE message size, or payload, and a requiredminimum SNR correspond to each transport format. In UMTS, the UEdetermines before the transmission of the preamble whether a transportformat can be chosen for the transmission according to the estimatedinitial preamble transmit power, the required offset between preambleand the transport block, the maximum allowed or available UE transmitpower, a fixed offset and additional margin. The preamble in UMTS neednot contain any information regarding the transport format selected bythe EU since the network does not need to reserve time and frequencyresources and, therefore, the transport format is indicated togetherwith the transmitted message.

The eNB must be aware of the size of the message that the UE intends totransmit and the SNR achievable by the UE in order to select the correcttransport format upon reception of the preamble and then reserve thenecessary time and frequency resources. Therefore, the eNB cannotestimate the SNR achievable by the EU according to the received preamblebecause the UE transmit power compared to the maximum allowed orpossible UE transmit power is not known to the eNB, given that the UEwill most likely consider the measured path loss in the DL or someequivalent measure for the determination of the initial preambletransmission power.

The eNB could calculate a difference between the path loss estimated inthe DL compared and the path loss of the UL. However, this calculationis not possible if power ramping is used and the UE transmit power forthe preamble does not correspond to the initially calculated UE transmitpower. Furthermore, the precision of the actual UE transmit power andthe transmit power at which the UE is intended to transmit is very low.Therefore, it has been proposed to code the path loss or CQI estimationof the downlink and the message size or the cause value in the UL in thesignature.

Self-organizing networks (SON) enhancements are necessary for theinteroperability of the existing features as well as for the newfeatures and new deployments considered in 3GP LTE rel-12. In 3GPP LTErel-11, mobility robustness optimization (MRO) has been enhanced toidentify for which UE type the failure has occurred. Other SON use casesmight require similar enhancements. For example, mobility load balancing(MLB) is not able to distinguish between UEs that support cell rangeexpansion (CRE) and non-CRE UEs.

Active antennas allow the creation of multiple vertical and horizontalbeams making the deployment dynamic. That enables dynamic cellsplitting/merging to handle changing load conditions. For example, beamsmay be steered to distribute capacity precisely according to actualtraffic mix, traffic location and user demands. That makes activeantennas particularly good for suburban and rural areas, where fixeddeployment of pico cells is expensive, but the network may facecongestion situations nonetheless. SON can automate the networkdeployment based on active antennas.

SON enhancements and new features for the deployments based on activeantenna system (AAS) have been discussed. Possible deployment scenariosof an AAS, and additionally required SON features for the AAS needs tobe discussed.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for transmitting acell shaping indication in a wireless communication system. The presentinvention provides a method for notifying neighbor eNodeBs (eNBs) of aplan of cell shaping or cell un-shaping, or an event that its cells havecompleted the cell shaping or the cell un-shaping.

In an aspect, a method for transmitting, by a first eNodeB (eNB), a cellshaping indication in a wireless communication system is provided. Themethod includes transmitting a cell shaping indication which indicatescell shaping of a cell, managed by the first eNB, in an active antennasystem (AAS) to a second eNB. The cell shaping means that main coverageof the cell is maintained unchanged but an edge of the cell can beadapted to load demand.

The cell shaping indication may indicate that the cell shaping of thecell has been completed. The method may further include performing thecell shaping of the cell before transmitting the cell shaping indicationto the second eNB.

The cell shaping indication may indicate that the cell shaping of thecell will be performed. The method may further include performing thecell shaping of the cell after transmitting the cell shaping indicationto the second eNB.

In another aspect, a method for transmitting, by a first eNodeB (eNB), acell un-shaping indication in a wireless communication system isprovided. The method includes transmitting a cell un-shaping indicationwhich indicates cell un-shaping of a cell, managed by the first eNB, inan active antenna system (AAS) to a second eNB. The cell un-shapingmeans that coverage of the cell goes back to original coverage.

The cell un-shaping indication may indicate that the cell un-shaping ofthe cell has been completed. The method may further include performingthe cell un-shaping of the cell before transmitting the cell un-shapingindication to the second eNB.

The cell un-shaping indication may indicate that the cell un-shaping ofthe cell will be performed. The method may further include performingthe cell un-shaping of the cell after transmitting the cell un-shapingindication to the second eNB.

In another aspect, a method for rejecting, by a first eNodeB (eNB), ahandover procedure in a wireless communication system is provided. Themethod includes determining to perform cell un-shaping of a cell managedby the first eNB, wherein the cell un-shaping means that that coverageof the cell goes back to original coverage, receiving a handover requestmessage from a second eNB right after determining to perform the cellun-shaping of the cell, and transmitting a handover preparation failuremessage including cause information, which indicates the cell un-shapingof the cell.

Cell shaping or cell un-shaping can be notified to neighbor eNBs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and atypical EPC.

FIG. 3 shows a block diagram of a user plane protocol stack and acontrol plane protocol stack of an LTE system.

FIG. 4 shows an example of a physical channel structure.

FIG. 5 shows a scenario of beam forming for adjustments for an AAS.

FIG. 6 shows a scenario of cell shaping for adjustments for an AAS.

FIG. 7 shows a scenario of cell splitting for adjustments for an AAS.

FIG. 8 shows an example of a method for transmitting an indicationaccording an embodiment of the present invention.

FIG. 9 shows another example of a method for transmitting an indicationaccording an embodiment of the present invention.

FIG. 10 shows another example of a method for transmitting an indicationaccording an embodiment of the present invention.

FIG. 11 shows an example of a cell shaping operation among neighboreNBs.

FIG. 12 shows an example of a method for transmitting a cell shapingindication according to an embodiment of the present invention.

FIG. 13 shows an example of a method for transmitting a cell un-shapingindication according to an embodiment of the present invention.

FIG. 14 shows an example of a method for rejecting a handover procedureaccording to an embodiment of the present invention.

FIG. 15 shows a wireless communication system to implement an embodimentof the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is an evolution of IEEE 802.16e, and provides backwardcompatibility with an IEEE 802.16-based system. The UTRA is a part of auniversal mobile telecommunication system (UMTS). 3rd generationpartnership project (3GPP) long term evolution (LTE) is a part of anevolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses the OFDMA indownlink and uses the SC-FDMA in uplink. LTE-advance (LTE-A) is anevolution of the 3GPP LTE.

For clarity, the following description will focus on the LTE-A. However,technical features of the present invention are not limited thereto.

An active antenna system (AAS) refers to a base station (BS) equippedwith an antenna array system, the radiation pattern of which may bedynamically adjustable. The AAS introduces an alternative antenna systemfrom the one installed in the conventional BS. The interactions betweenthe antenna array system and the transmitters and receivers within theAAS might be different from the conventional BS and the conventionalantenna system.

AAS deployment scenarios are described. It may be referred to Section 5of 3GPP

1) Tilt and Radiation Pattern Control

Antennas are usually manufactured with a fixed beamwidth, and antennamanufacturers typically offer a limited number of beamwidth variationswithin their conventional product lines. Conventional BS installationsoften introduce physical tilt to the antenna in order to orient the mainlobe of the antenna response towards the ground. Antenna tilt isselected to optimize desired cell coverage and to minimize interferenceto and from adjacent cells. Some installations employ remote electricaltilt (RET) devices which allow adjustment of the phase shift tofacilitate remote control of the antenna tilt angle.

An AAS may dynamically control the elevation and azimuth angles, as wellas the beamwidth of its radiation pattern via electronic means.Electronic control may be used along with mechanical control. The AASradiation pattern may be adapted to the specific deployment scenario andpossibly to changing traffic patterns. The AAS radiation pattern mayalso be independently optimized for different links such asindependently for uplink and downlink, for coverage and beam forminggain purposes.

The concepts of tilt and beamwidth control can be extended by atechnique known as cell partitioning in which the cell is subdivided invertical or horizontal directions by adjustment of the antenna pattern.For example, one cell partition is located close to the BS and the othercell partition is located farther away from the BS.

2) Multiple-Input Multiple-Output (MIMO)

MIMO is a general terminology that includes the various spatialprocessing techniques such as beamforming, diversity, and spatialmultiplexing. Brief description of each is provided below.

-   -   Beamforming: The use of a dedicated beam formed towards the UE        when data demodulation using a dedicated reference signal is        supported by the UE.    -   Diversity: The use of diversity techniques to jointly optimize        in the spatial and frequency domain through the use of, for        example, spatial-frequency block code (SFBC) or frequency        switching transmit diversity (FSTD), or combinations of both.    -   Spatial multiplexing: The transmission of multiple signal        streams to one (SU-MIMO) or more (MU-MIMO) UEs using multiple        spatial layers created by combinations of the available        antennas.

3) Differentiated Antenna Behaviors at Different Carrier Frequencies

AAS supports the use of different antennas at different carrierfrequencies and for different radio access technologies (RATs). Forexample, an AAS may create 4 virtual antennas for an LTE carrier and 2antennas for a GSM or high-speed packet access (HSPA) carrier.

4) Per RB (or UE) Transmission and Reception

Each UE may get its own beam that tracks the movement of the UE. Thecurrent specification support for spatial multiplexing, beamforming andtransmit diversity includes the ability to schedule transmission andreception to one UE within one resource block. This allows beamformingto individual UEs with adaptation to mobility, as an example.

The AAS BS can be deployed for wide area, medium range, and local areacoverage.

-   -   The wide area coverage deployment scenario is typically found in        outdoor macro environments, where the BS antennas are located on        masts, roof tops or high above street level. An AAS BS designed        for wide area coverage is called a macro AAS.    -   The medium range coverage deployment scenario is typically found        in outdoor micro environments, where the AAS BSs are located        below roof tops. An AAS BS designed for medium range coverage is        called a micro AAS.    -   The local area BS deployment scenario is typically found indoors        (offices, subway stations, etc.) where antennas are located on        ceilings or walls. Deployment scenarios for local area coverage        can also be found outdoors in hot spot areas like marketplaces,        high streets or railway stations. An AAS BS designed for local        area coverage is called a pico AAS.

The radiation pattern for an AAS BS can be dynamically adjustable, whilea fixed beam pattern is assumed for the conventional BS. Coexistence ofan AAS BS with a conventional BS based on an un-coordinated deploymentshall be considered. Analytical approaches can be used to study thecoexistence requirements based on existing results, supplemented withadditional simulations when necessary. The following initial scenariosare identified for the purpose of studying the spatial characteristicsfor AAS BS:

-   -   E-UTRA macro AAS BS co-located with another E-UTRA macro AAS BS    -   E-UTRA macro AAS BS co-located with E-UTRA macro legacy BS

Based on the deployment/coexistence scenarios described above, thedeployments scenarios of AAS may be categorized on three aspects asdescribed in Table 1 below.

TABLE 1 Amount of development required Possible scenarios further Cellsplit to two parts (inner area and outer area) medium partitioning trackthe movement of each UE high Frequency identical frequency for allpartition in a cell medium and RAT different frequency for eachpartition medium assignment different RAT for each partition highCoexistence macro AAS BS co-located with another medium scenarios macroAAS BS macro AAS BS co-located with macro medium legacy BS

Referring to Table 1, related to the cell partitioning, splitting a cellto inner part and outer part is considered as a basic deploymentscenario. If more accurate and adaptive beam steering is assumed, per UEtransmission and reception by tracking each UE's movement would bepossible scenario.

Related to frequency and RAT assignment for each cell partition, thereare three possible options: 1) assigning an identical frequency for allpartition, 2) different frequency for each partition, and 3) differentRAT for each partition. Among three options, assigning different RAT foreach partition may require more efforts in the network point of viewthan other options, e.g., inter-RAT handover, cell identifier (ID)allocation, and need more discussion about use cases.

Related to the coexistence scenarios, if the interworking SON mechanismsbetween

AAS BSs co-located with each other are developed, then it can be usedfor the case of AAS BS co-located with legacy BS. However in this casethe compatibility problems should be considered.

Therefore, it is preferable to focus on the following AAS deploymentscenarios first.

-   -   splitting cell to inner area and outer area,    -   assigning identical frequency for all partition in a cell or        different frequency for each partition, and    -   macro AAS BS co-located with another macro AAS BS.

Basic AAS deployment scenarios are described. For AAS actions that maybe applied to optimize capacity in case of high UE concentration,scenarios including beam forming, cell shaping, and cell splitting havebeen discussed. The scenarios assume high traffic demand from highdensity of UEs. The UEs may be concentrated temporarily or permanentlyin space. The AAS-based deployment is used to optimize capacity.

FIG. 5 shows a scenario of beam forming for adjustments for an AAS. Thebeam forming introduces adaptive or reconfigurable antenna systems,where the coverage of each cell is maintained unchanged. Referring toFIG. 5, the eNB 1 configures antennas towards traffic hotspot. There isno cell edge interference according to the beam forming, and there is noUE mobility coordination in the traffic hotspot. Further, there is noserved/neighbor cell update and/or features reconfigurations in eacheNB. Further, there is not configuration update in operations,administration and maintenance (OAM). The same physical cell identity(PCI) is used in all the cell coverage. These adjustments are consideredto be on fast time scale (following radio resource management (RRM)).The trigger for the change may be OAM reconfiguration (e.g., based oncollected key performance indicators (KPIs)) if beam forming results inre-shaping cell coverage or, if the cell coverage is not affected, thecontrol unit is the base station (implementation based).

FIG. 6 shows a scenario of cell shaping for adjustments for an AAS. Thecell shaping introduces adaptive or reconfigurable antenna systems,where the main coverage of each cell is maintained unchanged but thecell edge can be adapted to load demand. Referring to FIG. 6, the cell 1is shaped around traffic hotspot. There is no cell edge interferenceaccording to the cell shaping, and there is no UE mobility coordinationin the traffic hotspot. Further, there is no served/neighbor cell updateand/or features reconfigurations in each eNB. Further, there is notconfiguration update in OAM. The same PCI is used in all the cellcoverage. These adjustments are considered to be on medium time scale(every 1 h or more seldom). The trigger for the change may be OAMreconfiguration (e.g., based on collected KPIs) or the control unit maybe the base station (implementation based) if the change is pre-planned.

FIG. 7 shows a scenario of cell splitting for adjustments for an AAS.The cell splitting adopts higher order sectorization (vertical,horizontal or a combination) to selected base stations by changing anantenna system to include more antenna beams, each covering a smallerarea than before the change. However, the main coverage of the combinedbeams corresponds to the main cell coverage before the split. Referringto FIG. 7, the cell 1 is split into cell 1 a and cell 1 b in order tosupport traffic hotspot. Cell edge interference may occur between thecell 1 a and cell 1 b, and mobility of UEs connected to the cell 1 intraffic hotspot may be changed.

Further, served/neighbor cell update, which includes automatic neighborrelation (ANR), PCIs, neighbor cell list (NCL), etc., and featuresreconfigurations, which include mobility robustness optimization (MRO),enhanced inter-cell interference coordination (eICIC), etc., may beperformed in each eNB. Further, there may be new configuration update inOAM. Each of the beams broadcasts different PCI. Cell splittingprocedures is considered on a long term time scale (every 1 h or moreseldom—few times a day). The trigger for the change may be OAMreconfiguration (e.g., based on collected KPIs) or, if the cell coverageis not affected and the split is pre-planned, the control unit is thebase station (implementation based). Indication of the cell splittingmay be needed at OAM and neighbor eNBs.

Hereinafter, a scenario of cell shaping is focused according to anembodiment of the present invention.

Based on the approach describe above, there are some issues whichrequire enhancements of the current specifications regarding the MROmechanisms. That is, UE needs to distinguish cells supporting a cellshaping function by the AAS from normal cells because the cell shapingfunctions causes the change of cell coverage area dynamically. Eventhough the UE is handed over to the shaping part of a cell, the UE mayhave to leave the cell due to the dynamic change of cell coverage.Therefore when the eNB decides a handover of the UE, the eNB needs toknow about whether the target cell supports the cell shaping function bythe AAS or not.

Accordingly, according to an embodiment of the present invention, an eNBmay indicate whether the cell supports a cell shaping function by theAAS or not. Upon receiving the indication, the serving eNB may knowwhether the neighbor cell, to which the serving eNB may handover the UE,supports the cell shaping function or not.

FIG. 8 shows an example of a method for transmitting an indicationaccording an embodiment of the present invention. Referring to FIG. 8,the neighbor eNB broadcasts the indication related to its own cells toUEs via a radio channel. Then, upon receiving the indication, the UEreports the received indication to the serving eNB. Accordingly, theserving eNB may know whether the neighbor cell supports the cell shapingfunction or not.

FIG. 9 shows another example of a method for transmitting an indicationaccording an embodiment of the present invention. Referring to FIG. 9,the neighbor eNB broadcasts the indication related to its own cells toUEs via a radio channel. If the received indication includes informationthat the neighbor cell is supporting the cell shaping function by theAAS, then the UE does not report measurement results to the serving eNB.Accordingly, the UE cannot be handed over to the neighbor cell.

FIG. 10 shows another example of a method for transmitting an indicationaccording an embodiment of the present invention. Referring to FIG. 10,the neighbor eNB transmits the indication related to its own cells tothe serving eNB of the UE via the X2 interface. Accordingly, the servingeNB may know whether the neighbor cell supports the cell shapingfunction or not.

The serving eNB may consider the indication, which is obtained from theUE or the neighbor eNB, when it decides whether to handover the UE tothe cell related to the indication or not.

Further, according to an embodiment of the present invention, PCIs forcells supporting the cell shaping function by the AAS may be reserved.The eNB may broadcast the reserved PCI range information to its neighboreNBs. Table 2 shows an example of allocation of PCIs for the cellssupporting the cell shaping function by the AAS according to anembodiment of the present invention. For example, if the operatorreserves K+1 PCIs for the cells supporting the cell shaping function bythe AAS, the example of PCI assignment may be as follows.

TABLE 2 0 1 2 3 4 5 6 N N + 1 N + 2 . . . 499 500 PCI 7 8 9 10 11 . . .N + 3 . . . N + K 501 502 503 cells PCI range for normal PCI range forthe cells PCI range for cells supporting the cell normal cell. shapingfunction by AAS

Referring to Table 2, PCIs from N to N+K are reserved for the cellssupporting the cell shaping function by the AAS, and the remaining PCIsare reserved for the normal cells. PCTs reserved for the cellssupporting the cell shaping function by the AAS and PCIs reserved forthe normal cells do not overlap.

Further, according to an embodiment of the present invention, when acell (cell 1) is in the heavy traffic load status, the eNB (eNB 1)managing the cell 1 may request its neighbor eNB (eNB 2) to shape a cell(cell 2) of the neighbor eNB toward the cell 1 in order to accept UEs ofcell 1.

FIG. 11 shows an example of a cell shaping operation among neighboreNBs. Referring to FIG. 11, the cell 1 managed by the eNB1 is shapedtowards the cell 2 managed by the eNB 2 at the edge of the cell. Maincoverage of the cell 1 is unchanged. By shaping the cell 1 towards thecell 2 and accepting UEs of the cell 2, if the amount of the requiredtraffic (or, the number of UEs) in the cell 2 is high, the eNB 2 canescape from the heavy load status. Moreover, if the cell 1 is in theheavy load status, it is possible that the eNB 2 shapes the cell 2towards the cell 1 and accepts UEs of the cell 1.

The problem is that the practical cell coverage before the cell shapingwould be different with the coverage area after the cell shaping.Therefore, if the eNB plans for the cell shaping or the cell un-shapingof its cells, it should notify neighbor cNBs of its plan. Alternatively,the eNB should announce neighbor eNBs the event that its cells havecompleted the cell shaping or the cell un-shaping. Hereinafter, the cellshaping means that the main coverage of the cell is maintained unchangedbut the cell edge can be adapted to load demand. The cell un-shapingmeans that that the shaping cell goes back to the original status. Thatis, the cell shaping may be an operation from FIG. 11-(a) to FIG.11-(b), and the cell un-shaping may be an operation from FIG. 11-(b) toFIG. 11-(a).

FIG. 12 shows an example of a method for transmitting a cell shapingindication according to an embodiment of the present invention.

Referring to FIG. 12-(a), in step S100, the eNB1 decides to perform cellshaping of a cell and performs the cell shaping of the cell. In stepS101, the eNB1 transmits a cell shaping indication which indicates thatthe eNB1 has performed the cell shaping of the cell. Accordingly, theeNB1 may inform the eNB2 the event that the eNB1 completed to the cellshaping of the cell.

Referring to FIG. 12-(b), in step S110, the eNB1 decides to perform cellshaping of a cell. In step S111, the eNB1 transmits a cell shapingindication which indicates that the eNB1 will perform the cell shapingof the cell. Accordingly, the eNB1 may inform the eNB2 the plan of thecell shaping of the cell after making the cell shaping decision. In stepS112, the eNB1 performs the cell shaping of the cell.

FIG. 13 shows an example of a method for transmitting a cell un-shapingindication according to an embodiment of the present invention.

Referring to FIG. 13-(a), in step S200, the eNB1 decides to perform cellun-shaping of a cell and performs the cell un-shaping of the cell. Instep S201, the eNB1 transmits a cell un-shaping indication whichindicates that the eNB1 has performed the cell un-shaping of the cell.Accordingly, the eNB1 may inform the eNB2 the event that the eNB1completed to the cell un-shaping of the cell.

Referring to FIG. 13-(b), in step S210, the eNB1 decides to perform cellun-shaping of a cell. In step S211, the eNB1 transmits a cell un-shapingindication which indicates that the eNB1 will perform the cellun-shaping of the cell. Accordingly, the eNB1 may inform the eNB2 theplan of the cell un-shaping of the cell after making the cell un-shapingdecision. In step S212, the eNB1 performs the cell un-shaping of thecell.

Moreover, right after an eNB decides to the cell un-shaping of its cell,if the eNB receives the HANDOVER REQUEST message from its neighbor eNB,then the eNB needs to reject the handover request in order to prevent ahandover failure, and inform the appropriate rejection cause to itsneighbor eNB.

FIG. 14 shows an example of a method for rejecting a handover procedureaccording to an embodiment of the present invention.

Referring to FIG. 14-(a), in step S300, the eNB1 decides to perform cellun-shaping of a cell. In step S301, the eNB2 decides a handover, andaccordingly, in step S302, the eNB2 transmits the HANDOVER REQUESTmessage to the eNB1. That is, the eNB1 receives the HANDOVER REQUESTmessage from the eNB2 right after the eNB1 decided to perform the cellun-shaping of the cell. Therefore, in step S303, the eNB1 transmits theHANDOVER PREPARATION FAILURE message to the eNB2 with the causeinformation to indicate that the target cell (e.g., cell of the eNB1)has the plan of the cell un-shaping. In step S304, the eNB1 performs thecell un-shaping of the cell. In step S305, the eNB1 transmits a cellun-shaping indication which indicates that the eNB1 has performed thecell un-shaping of the cell. Accordingly, the eNB1 may inform the eNB2the event that the eNB1 completed to the cell shaping of the cell.

Referring to FIG. 14-(b), in step S310, the eNB1 decides to perform cellun-shaping of a cell. In step S311, the eNB2 decides a handover, andaccordingly, in step S312, the eNB2 transmits the HANDOVER REQUESTmessage to the eNB1. That is, the eNB1 receives the HANDOVER REQUESTmessage from the eNB2 right after the cNB1 decided to perform the cellun-shaping of the cell. Therefore, in step S313, the eNB1 transmits theHANDOVER PREPARATION FAILURE message to the eNB2 with the causeinformation to indicate that the target cell (e.g., cell of the eNB1)has the plan of the cell un-shaping. In step S314, the eNB1 transmits acell un-shaping indication which indicates that the eNB1 will performthe cell un-shaping of the cell. Accordingly, the eNB1 may inform theeNB2 the plan of the cell shaping of the cell after making the cellshaping decision. In step S315, the eNB1 performs the cell un-shaping ofthe cell.

FIG. 15 shows a wireless communication system to implement an embodimentof the present invention.

A first eNB 800 includes a processor 810, a memory 820, and a radiofrequency (RF) unit 830. The processor 810 may be configured toimplement proposed functions, procedures, and/or methods in thisdescription. Layers of the radio interface protocol may be implementedin the processor 810. The memory 820 is operatively coupled with theprocessor 810 and stores a variety of information to operate theprocessor 810. The RF unit 830 is operatively coupled with the processor810, and transmits and/or receives a radio signal.

A second eNB 900 includes a processor 910, a memory 920 and an RF unit930. The processor 910 may be configured to implement proposedfunctions, procedures and/or methods described in this description.Layers of the radio interface protocol may be implemented in theprocessor 910. The memory 920 is operatively coupled with the processor910 and stores a variety of information to operate the processor 910.The RF unit 930 is operatively coupled with the processor 910, andtransmits and/or receives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The RF units 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

1-15. (canceled)
 16. A method for transmitting, by a first base station,a coverage modification indicator in a wireless communication system,the method comprising: transmitting, to a second base station, a firstcoverage modification indicator indicating a plan of coveragemodification of a cell, managed by the first base station, in an activeantenna system (AAS); and after transmitting the first coveragemodification indicator to the second base station, performing thecoverage modification of the cell managed by the first base station. 17.The method of claim 16, further comprising: before transmitting, to thesecond base station, a second coverage modification indicator indicatingthat a coverage of the cell, managed by the first base station, has beenmodified in the ASS, performing the coverage modification of the cellmanaged by the first base station; and transmitting the second coveragemodification indicator to the second base station.
 18. The method ofclaim 16, further comprising: deciding to perform the coveragemodification of the cell in the AAS.
 19. The method of claim 18, whereinthe first coverage modification indicator is transmitted to the secondbase station after deciding to perform the coverage modification of thecell in the AAS.
 20. The method of claim 16, wherein the coveragemodification is a cell shaping which means that main coverage of thecell is maintained unchanged but an edge of the cell can be adapted toload demand
 21. The method of claim 16, wherein the coveragemodification is a cell un-shaping which means that the first basestation returns a modified shape of the cell to its original shape. 22.A first base station transmitting a coverage modification indicator in awireless communication system, the base station comprising: a memory; atransceiver; and a processor, to connect the memory and the transceiver,that: controls the transceiver to transmit, to a second base station, afirst coverage modification indicator indicating a plan of coveragemodification of a cell, managed by the first base station, in an activeantenna system (AAS); and after transmitting the first coveragemodification indicator to the second base station, performs the coveragemodification of the cell managed by the first base station.
 23. Thefirst base station of claim 22, the processor that: before transmitting,to the second base station, a second coverage modification indicatorindicating that a coverage of the cell, managed by the first basestation, has been modified in the ASS, performs the coveragemodification of the cell managed by the first base station; and controlsthe transceiver to transmit the second coverage modification indicatorto the second base station.
 24. The first base station of claim 22, theprocessor that: decides to perform the coverage modification of the cellin the AAS.
 25. The first base station of claim 24, wherein the firstcoverage modification indicator is transmitted to the second basestation after deciding to perform the coverage modification of the cellin the AAS.
 26. The first base station of claim 22, wherein the coveragemodification is a cell shaping which means that main coverage of thecell is maintained unchanged but an edge of the cell can be adapted toload demand
 27. The first base station of claim 22, wherein the coveragemodification is a cell un-shaping which means that the first basestation returns a modified shape of the cell to its original shape.